Notes:
Mechanical creep and creep recovery in small shearing deformations have been studied in unligated clots formed with both thrombin and ancrod. In thrombin clots, both A binding sites (which interact with “a” sites to link monomer units within a protofibril) and B sites (which interact with “b” sites to form links between protofibrils) are exposed to enable formation of linkages; in ancrod clots, only the A sites are exposed. Fine clots (with minimal lateral aggregation of protofibrils), coarse clots (with substantial aggregation of fibril bundles), and clots of intermediate coarseness were compared. Fine thrombin clots showed less creep at short times but more creep at long times than coarse or intermediate clots and had more irrecoverable deformation relative to the initial elastic deformation. Ancrod clots had greater irrecoverable deformation than the corresponding thrombin clots, both fine and coarse. The permanent deformation in fine ancrod clots was enormous, corresponding almost to fluid character; the rate of permanent deformation was larger than that in fine thrombin clots by more than two orders of magnitude. For all types of clots, differential measurements of compliance (or its reciprocal, elastic modulus), as well as the applicability of the Boltzmann superposition principle to calculation of creep recovery, showed that the overall density of structure remained constant throughout the mechanical history; i.e., if structural elements were breaking, they were reforming at the same rate in different configurations. The possibility that the weakness of ancrod clots is attributable to partial degradation of α-chains rather than absence of Bb linkages was eliminated by comparisons of clots made with thrombin, ancrod, and ancrod plus thrombin; the last two showed identical partial degradation of α-chains (by gel electrophoresis), but the first and third had essentially identical initial elastic moduli and creep behavior. Two alternative mechanisms for irrecoverable deformation in fine clots are discussed, involving rupture of protofibrils and slippage of twisted segments, respectively.

Notes:
The scattering behaviour and the critical conditions where gelation takes place have been calculated for polycondensates formed under constraints. The general model includes fully random and stringently restricted reactions as limiting cases. Also polycondensates of glycerine-type monomers are included as special cases. The particle scattering factors of the f-functional random polycondensates differ remarkably from those polycondensates formed under strict constraints. The former show a Kratky plot of a simple curve, independent of the magnitude of the molecular weight and the number of functional groups, and the curve approaches a constant asymptote of u2·Pz(u)=3, the latter exhibits a maximum at u2=6 which becomes more pronounced with increasing molecular weight, (u2 = 〈S2〉zh2, with h, the value of the scattering vector). The scattering curves of the polycondensates formed under weak constraints show at low molecular weights the same behaviour as those formed under stringent constraints, but approach the behaviour of random polycondensates at large molecular weights. The scattering curves of the glycerine-type polycondensates show no deviations in shape from random polycondensates.

Notes:
Poly(diacetylene)s dissolved in common organic solvents undergo random chain scission, if irradiated by UV-light. The pure polymers and their solutions are, however, stable, if they are photoirradiated within the main-absorption band of the polymer backbone. The usual triplet sensitizers, especially in the presence of oxygen, and radical donors such as 2,2′-azoisobutyronitrile (AIBN) enhance the rate of photodegradation. Suitable dyes are able to sensitize the chain-scission in the visible regions as well. Random chain scission occurs also in the dark, but only at temperatures above room temperature and is enhanced by the addition of radical-donors, e.g. AIBN. A mechanism of chain scission, induced by the attack of a radical to a multiple bond of the polyconjugated backbone of the polymer is proposed.

Notes:
The commercially available poly(1-octenylene) Vestenamer® formed by the metathetic polymerization of cyclooctene with a tungsten catalyst, is highly crystalline at room temperature; it shows specific properties as a blend component, thus favourably influencing the processing characteristics and the final product quality. Differential scanning calorimetry, infrared and torsion pendulum experiments indicate that the melting temperature and the degree of crystallinity depend on the concentration of trans double bonds, on their distribution along the polymer chain as well as on the sample history. The formation of crosslinks induced by very intensive UV irradiation of 100 μm thin films leads to a reduction of the melting temperature and the crystallinity. A correlation between stiffness (shear modulus G′) and crystallinity was found for samples with varying amounts of trans double bonds.

Notes:
Statistical and block copolymers of decyl (DMA) and methyl methacrylate (MMA) were synthesized via group transfer polymerization (GTP) and characterized by size exclusion chromatography (SEC) and gradient HPLC. For HPLC a normal-phase solvent gradient of isooctane and THF was used; the chromatograms were recorded by evaporative light scattering detection (ELSD). The block copolymers were shown to contain substantial amounts of precursor homopolymer by gradient elution, even in those cases where SEC furnished a perfectly monomodal molecular weight distribution (MWD). Comparison of the respective HPLC elution characteristics demonstrated that block copolymers are more strongly retained than statistical copolymers of identical composition. Whereas the latter are eluted according to chemical composition, the elution of the block copolymers seems to be controlled by the length of the poly(MMA) block.

Notes:
Measurements of stress relaxation in uniaxial extension have been made on fibrin film prepared from fine bovine fibrin clots (i.e., clots in which there is minimal lateral aggregation of protofibrils), both ligated and unligated, and polymerized with both thrombin and ancrod, plasticized with either aqueous buffer or glycerol. The stress 100 s after imposition of strain was approximately proportional to In λ, where λ is the stretch ratio. Ligated thrombin films showed comparatively little relaxation over a period of one day and almost complete recovery after release of stress. In unligated thrombin films, there was substantial relaxation in two stages, as previously observed for coarse films, and substantial irrecoverable deformation. The extent of relaxation and the proportion of strain that was irrecoverable increased with the magnitude of the strain. In ancrod films (unligated), there was much more relaxation (stress decaying by as much as a factor of 10) and much more irrecoverable deformation (about 70% of the initial deformation); these results did not depend on the magnitude of the strain. When an ancrod film was released after relaxation and submitted to a second stretch, the extent of the second relaxation was much less. These observations are discussed in relation to the structure of fine films and possible mechanisms for relaxation and irrecoverable deformation.

Notes:
Measurements of small-angle x-ray scattering have been made on films prepared from fine and coarse (i.e., formed at high and low, respectively, pH and ionic strength) clots of bovine fibrin by osmotic shrinkage or compression in one dimension. Intensity profiles were obtained with pinhole geometry on films stretched up to a stretch ratio of 1.43. In unstretched coarse films, repeat spacings were seen at about 245, 120, and 77-80 Å. These peaks can probably be identified with the first, second, and third orders of the well-known fibrin repeat of 225 Å. In unstretched fine films, only the 77-80 Å spacing was seen. In this case, the first two orders may be weak because the half-staggered arrangement of monomer units giving rise to the 225 Å reflection is not reinforced by lateral aggregation of protofibrils; the third order may be strong since the molecular subdomains appear to divide the repeat roughly into thirds. After stretching, the 77-80 Å spacing persisted in the meridional direction but almost disappeared in the equatorial. Experiments on unstretched films prepared with ancrod substituted for thrombin gave similar results.